Method for making cube-on-edge texture in high purity silicon-iron



United States Patent 3,105,781 METHGD FOR MAKING CUBE-ON-EDGE TEX- TUREIN HIGH PURITY SILICGN-ERQN John L. Walter, Scotia, N.Y., assignor toGeneral Electric tCompany, a corporation of New York No Drawing. FiledMay 2, 1960, Ser. No. 25,840 4 Claims. c1. 148-111) This inventionrelates to grain-oriented magnetic alloys and more particularly to animproved method for producing bodies of iron-base magnetic alloys havinga majority of the grains oriented in (110) [001] or cube-onedgecrystalline orientation to provide at least one direction of easiestmagnetization.

This application is a continuation-in-part of copending applicationSerial No. 859,847, filed December 16, 1959, now abandoned, and assignedto the same assignee as the present invention.

Various procedures and processes have been used in the past to producesheet and strip materials from siliconiron, aluminum-iron,molybdenum-iron alloys and combinations of these alloys in which thebodies have a cubeon-edge orientation providing an easiest direction ofmagnetization. Generally, the basic concept behind the prior artprocesses has been to retain a small grain size during the hot rollingstages through the use of a dispersed second phase. The dispersed secondphase prevents any appreciable grain growth from occurring during hotrolling and during annealing between cold rolling stages. It is notuntil the application of a final texture-developing anneal that thesecond phase is either removed or dissolved and grain growth isefiected.

Although the (110) [001] or cube-on-edge crystalline orientation is wellknown in the art in electrical sheet steels and is referred to in manystandard texts, the following explanation of the orientation is includedfor the sake of clarity. The orientation may be described as one inwhich the unit cube lattices of the oriented grains have a planecontaining diagonally-opposite cube edges substantially parallel to theplane of the sheet and a pair of opposite cube faces substantiallyperpendicular to the rolling direction and to the plane of the sheet.The (110) [001] designation is based upon the Miller CrystallographicIndex System, a complete discussion of which may be found in Structureof Metals, C. S. Barrett, second edition, 1952, pages 1-25, published bythe Macmillan Company. Material having this orientation is anisotropicand has optimum magnetic properties in the [001] direction parallel tothe direction of rolling, the magnetic properties transverse to thedirection of rolling being inferior to those of the rolling direction.

It is a principal object of this invention to provide a novel processfor producing a (110) [001] grain orientation in iron-base magneticalloys of high purity.

Another object of this invention is to provide a process for producing acube-on-edge grain orientation in magnetic sheet material of up to about15 mils thickness Without the use of a grain growth inhibiting secondphase particle dispersion.

Another object of this invention is to provide a simpler and moreeconomical process for the production of magnetic sheet materials havingan easiest direction of magnetization.

Other objects and advantages of this invention will be in part obviousand in part explained by reference to the accompanying specification.

Generally, the present process comprises preparing an iron-base magneticalloy, containing not less than about 92 percent iron, and not more thanabout 0.2 weight percent incidental impurities, rolling the body to athickness of up to 15 mils, coating it with magnesia and then 3,105,781Patented Oct. 1, 1963 subjecting the coated body to an anneal in acleansing atmosphere for a length of time such that the coating willvaporize and the desired cube-on-edge orientation develop.

More specifically, the first step of the present process comprisespreparing a suitable iron-base magnetic alloy which contains not morethan about 0.2 weight percent total incidental impurities. Suitablealloys are those which contain from 2 to 6 percent silicon, up to 8percent aluminum, and up to 5 percent molybdenum, or some combination ofthese metals and which contain not less than about 92 weight percentiron. While the silicon-iron alloys are those with which the presentinvention is concerned, the substitution of aluminum and/ or molybdenumin whole or in part for silicon can be effected according towell-recognized existing practices.

Having prepared an alloy as just outlined and cast it into ingot form,the ingot is then heated to a temperature within the range of from about700 to 1200 C. and hot rolled, without any intermediate anneals betweenhot rolling stages to an intermediate or hot band thickness on the orderof about mils (0.100 inch). At the hot band stage, the material is onceagain reheated to a temperature of from about 700 to 1200 C. and thencooled to room temperature or slightly above, for example, up to 200 to300, then cold rolled to a thickness of up to about 15 mils (0.015inch). Once the material has been reduced to this sheet-like form byrolling, it is coated with a layer of magnesia, which layer isolates thecoated metal from the surrounding environment. The coated material issubjected to a final annealing in a cleansing atmosphere, specifically,either dry hydrogen having a dew point of no higher than-40 F. or vacuumcontaining no more than one micron of oxygen, for a period of timesufiicient to cause the magnesia layer to vaporize and to causeincreased growth of those grains which are oriented in the [001] crystalorientation. Generally, the final annealing temperature will be on theorder of from 1100 to 1300 C. and for periods of time of from 4 to 16hours. Obviously, these temperature ranges may be extended somewhat ineither direction by suitably varying the time periods, although theranges stated represent those which will normally be most eflective tocarry out the desired grain growth.

One of the important factors which is [felt to exert a controllingeffect upon the orientation obtained is the amount of oxygen present inthe thin strip material, that is, the material of up to 15 milsthickness. Generally speaking, the oxygen content in this material willbe above six parts per million but should not exceed 0.005 weightpercent (50 ppm.) if the cube-on-edge orientation is to be obtained. Ifthe impurity content is too high or the oxygen content is excessivelyhigh, grain growth will be retarded due to the presence of dispersedsecond phases present in the material and optimum texture andmagnetization properties cannot be obtained. If the oxygen is permittedto diffuse rapidly from the body to the surface of the material and ismaintained at the surface, a (l00)[001] or cube texture would result.Thus, the apparent function of the magnesia coating is to retard growthuntil the oxygen content of the metal is too low (about 6 ppm. or less)to permit growth of cube oriented grains. The oxygen from the bodyapparently remains in the magnesia coating. Finally, when the magnesiacoating vaporizes from the body, the cube-onedge orientation will resultby growth of (110) [001] grains.

In view of the fact that the oxygen content at the surface of the bodyexerts a controlling effect on the orientation, it is apparent that thecleansing environment used must not contain excessive amounts of oxygen.Generally, the oxygen content of the cleansing environment, viz.,hydrogen or vacuum, must be low enough to pre- 3 vent oxidation ofsilicon at the 1100 to 1300" C. annealing temperatures. If the oxygen isin excess of this amount, then the metal body is not loweredsufiiciently in oxygen content to develop the cube-onedge orientation.Dry hydrogen, that is, hydrogen having a dew point no higher than -40F., is acceptable as a cleansing atmosphere. Also, vacuum containing nomore than one micron of oxygen can be used efiec-tively. Obviously,atmospheres containing less oxygen, for example, a hydrogen atmosphereof 70 F. dew point, are completely acceptable, the former limitsrepresenting the boundaries.

As a specific example of a material produced according to the presentprocess, a silicon iron alloy containing 3 percent silicon was vacuummelted and cast into ingot shape. This material contained a totalimpurity content on the order of 0.006 percent by weight. The ingot wasthen heated to 1000 C., was then hot rolled to a band thickness of 100mils (0.100 inch) with no reheating between rolling stages. The band wasthen annealed at 700 C. for 5 hours in dry hydrogen ('-70 F.) and coldrolled in stages of reduction of 50 percent to 6 mils (0.006 inch).Between each cold reduction, the material was given an anneal at 900 C.for 30 minutes in dry hydrogen (-70 F.).

Following reduction of the band to 6 mil strip, the material waselectropolished to 5 mils (0.005 inch) to produce a smooth surface. Thiselectropolishing also had the effect of somewhat lowering the oxygencontent on the surface of the material and removing oxide and othercontaminating particles. In order to determine what the effect of themagnesia was, one sample was prepared and coated with a layer of milk ofmagnesia while the other sample was left entirely uncoated. Both of thesamples were then placed on plates of high purity alumina, to preventany contamination, and heated to 1230 C. at a heating rate of 100 C. perhour. The samples were held at this temperature for a period of 8 hoursin dry hydrogen ('70 F.). While dry hydrogen was used in this instance,it is also possible to use a vacuum environment and obtain the sameresults, as already described.

The secondary crystals of the uncoated sample had a cube or (100) [001]grain orientation, whereas the coated sample, which also contained alarge number of secondary crystals, had a majority of the grainsoriented in the (110) [001] orientation. Approximately 70 percent of thegrains in the coated sample were in the (110) [001] orientation.Further, X-ray examination of 12 of the secondary crystals of the coatedsample showed that for all the crystals examined, a (110) plane lieswithin 5 of parallel to the plane of the sheet and a [001] directionlies within 5 of the rolling direction.

Thus, the present process makes possible the. production of a magneticsheet material in which a majority of the grains have the cube-on-ed georientation and are oriented within about '5 of the rolling directionused to produce the strip material.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. The method of producing an alloy body having a majority of the grainsoriented in the (1?10)[001] crystal orientation comprising, providing aninitial cold rolled body of up to 15 mils thickness and consisting of atleast 92 weight percent iron, 2 to 6 weight percent silicon, up to about8 weight percent aluminum, up to about 5 weight percent molybdenum andfrom not less than 6 to not more than 50 parts per million of oxygen andcontaining not more than about 0.2 Weight percent total incidentalimpurities, which impurities do not form a second phase dispersioneffectively restricting grain growth, applying a coating of magnesia tothe exposed surfaces of the body isolating the surfaces from thesurrounding environment, and annealing the coated body in an environmentselected front the group consisting of hydrogen having a dew point nohigher than 40 F. and vacuum containing no more than one micron ofoxygen at a temperature of from about 1100 to 1300 C. for a period oftime suflicient to vaporize the coating from. the body and orient amajority of the grains in the (110) [001] orientation.

2. The method of producing an alloy body having a majority of the grainsoriented in the (110) [001] crystal orientation comprising, providing aninitial cold rolled body of up to 15 mils thickness consistingessentially of 2 to 6 weight percent silicon, remainder substantiallyall iron, and from not less than 6 to not more than 50 parts per millionof oxygen and containing not more than about 0.2 weight percent totalincidental impurities, which impurities do not form a second phasedispersion effect-ively restricting grain growth applying a coating ofmagnesia to the exposed surfaces of the body isolating the surfaces fromthe surrounding environment, and annealing the coated body in a dryhydrogen environment having a dew point no higher than 40 F. at atemperature of from about 1100 to 1300" C. for from about 4 to 16 hoursto vaporize the magnesia coating from the body and orient a majority ofthe grains in the (110) [001] orientation.

3. The method of producing a sheet-like alloy body having a majority ofthe grains oriented in the (110) [001] crystal orientation comprising,providing a cast alloy body consisting essentially of not less thanabout 92 weight percent iron, from about 2 to 6 weight percent silicon,up to about 8 weight percent aluminum, up to about 5 weight percentmolybdenum and from not less than 6- to not more than 50 parts permillion of oxygen and containing not more than about 0.2 weight percenttotal incidental impurities, which impurities do not form a second phasedispersion efiectively restricting grain growth, hot rolling said castbody at a temperature of from 700 to 1200 C. to an intermediatethickness of about mils, annealing said intermediate at an elevatedtemperature, cold rolling said annealed intermediate to a reduction ofabout 40 to 99.5 percent in substantially the same direction, usingintermediate anneals where required to produce a final cold rolled bodyof thickness not exceeding about 15 mils, applying a coating of magnesiato the exposed surfaces of the body isolating the surfaces from thesurrounding environment, and annealing the coated body in an environmentselected from the group consisting of hydrogen having a dew point nohigher than 40 F. and vacuum containing no more than one micron ofoxygen at a temperature from about 1100 to 1300 C. for a period of timesufficient to vaporize the coating from the body and orient a majorityof the grains in the [001] crystal orientation.

4. The method of producing a sheet-like alloy body having a majority ofthe grains oriented in the (110) [001] crystal orientation comprising,providing a cast alloy body consisting essentially of not less thanabout92 weight percent iron, from about 2, to 6 weight percent silicon,up to about 8 weight percent aluminum, up to about 5 weight percentmolybdenum and from .not less than 6 to not more than 50 parts permillion of oxygen and containing not more than about 0.2 weight percenttotal incidental impurities, which impurities do not form a second phasedispersion effectively restricting grain growth, hot rolling said castbody at a temperature of from 700 to 1200 C. to an intermediatethickness of about 100 mils, annealing said intermediate at an elevatedtemperature of from about 700 to 1200 C., cold rolling said annealedintermediate to a reduction of about 40 to 99.5 percent in substantiallythe same direction, using intermediate anneals where required to producea final body of thickness not exceeding about 15 mils, applying acoating of magnesia to the exposed surfaces References Cited in the fileof this patent UNITED STATES PATENTS Yensen Aug. 11, 1936 Cole et a1.Jan. 5, 1943 Langworthy Oct. 29, 1946 Fiedler et a1. June 7, 1960Hollomon June 14, 1960

4. THE METHOD OF PRODUCING A SHEET-LIKE ALLOY BODY HAVING A MAJORITY OFTHE GRAINS ORIENTED IN THE (110) 001! CRYSTAL ORIENTATION COMPRISING,PROVIDING A CAST ALLOY BODY CONSISTING ESSENTIALLY OF NOT LESS THANABOUT 92 WEIGHT PERCENT IRON, FROM ABOUT 2 TO 6 WEIGHT PERCENT SILICON,UP TO ABOUT 8 WEIGHT PERCENT ALUMINUM, UP TO ABOUT 5 WEIGHT PERCENTMOLYBDENUM AND FROM NOT LESS THAN 6 TO NOT MORE THAN 50 PARTS PERMILLION OF OXYGEN AND CONTAINING NOT MORE THAN ABOUT 0.2 WEIGHT PERCENTTOTAL INCIDENTAL IMPURITIES, WHICH IMPURITIES DO NOT FORM A SECOND PHASEDISPERSIOON EFFECTIVELY RESTRICTING GRAIN GROWTH, HOT ROLLING SAID CASTBODY AT A TEMPERATURE OF FROM 700 TO 1200*C. TO AN INTERMEDIATETHICKNESS OF ABOUT 100 MILS, ANNEALING SAID INTERMEDIATE AT AN ELEVATEDTEMPERATURE OFF FROM ABOUT 700 TO 1200*C., COLD ROLLING SAID ANNEALEDINTERMEDIATE TO A REDUCTION OF ABOUT 40 TO 99.5 PERCENT IN SUBSTANTIALLYTHE SAME DIRECTION, USING INTERMEDIATE ANNEALS WHERE REQUIRED TO PRODUCEA FINAL BODY OF THICKNESS NOT EXCEEDING ABOUT 15 MILS, APPLYING ACOATING OF MAGNESIA TO THE EXPOSED SURFACE OF THE BODY ISOLATING THESURFACES FROM THE SURROUNDING ENVIRONMENT, AND ANNEALING THE COATED BODYAT A TEMPERATURE FROM ABOUT 1100 TO 1300*C. IN A CLEANSING ENVIRONMENTNON-OXIDIZING TO SILICON FOR A PERIOD OF TIME SUFFICIENT TO VAPORIZE THECOATING FROM THE BODY AND ORIENT A MAJORITY OF THE GRAINS IN THE (110)001! CRYSTAL ORIENTATION.